U.S. patent number 4,725,522 [Application Number 06/919,517] was granted by the patent office on 1988-02-16 for processes for cold pressure fixable encapsulated toner compositions.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Marcel P. Breton, Kar P. Lok.
United States Patent |
4,725,522 |
Breton , et al. |
February 16, 1988 |
Processes for cold pressure fixable encapsulated toner
compositions
Abstract
A process for the preparation of cold pressure fixable toner
compositions which comprises (1) admixing a core component
comprised of pigment particles, a water insoluble organic solvent
and elastomeric materials with a shell monomer dissolved therein;
(2) dispersing the resulting mixture in a water phase containing a
stabilizing material; (3) hydrolyzing by heating the resulting
mixture; (4) subsequently affecting an interfacial polymerization
of the aforementioned mixture; and (5) thereafter optionally
washing the resulting toner composition.
Inventors: |
Breton; Marcel P. (Toronto,
CA), Lok; Kar P. (Sarnia, CA) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
25442222 |
Appl.
No.: |
06/919,517 |
Filed: |
October 16, 1986 |
Current U.S.
Class: |
430/137.11;
427/222 |
Current CPC
Class: |
G03G
9/09364 (20130101); G03G 9/09392 (20130101); G03G
9/09371 (20130101) |
Current International
Class: |
G03G
9/093 (20060101); G03G 011/00 () |
Field of
Search: |
;430/137,138,110
;427/218,222 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goodrow; John L.
Attorney, Agent or Firm: Palazzo; E. O.
Claims
What is claimed is:
1. A process for the preparation of cold pressure fixable toner
compositions which comprises (1) admixing a core component
comprised of pigment particles, a water insoluble organic solvent
and elastomer materials with a shell monomer dissolved therein; (2)
dispersing the resulting mixture in a water phase containing a
stabilizing material; (3) hydrolyzing by heating the resulting
mixture; (4) subsequently affecting an interfacial polymerization
of the aforementioned mixture; and (5) thereafter optionally
washing the resulting toner composition.
2. A process in accordance with claim 1 wherein heating for the
hydrolysis is accomplished at a temperature of from about 35 to
about 70 degrees Centigrade.
3. A process in accordance with claim 1 wherein the interfacial
polymerization is accomplished by heating.
4. A process in accordance with claim 3 wherein the heating
temperature is from about 70 to about 90 degrees Centigrade.
5. A process in accordance with claim 1 wherein washing is
accomplished for removal of the stabilizer.
6. A process in accordance with claim 1 wherein the resulting toner
composition is washed.
7. A process in accordance with claim 1 wherein the pigment
particles are selected from the group consisting of carbon black
and magnetites.
8. A process in accordance with claim 1 wherein the pigment
particles are comprised of a mixture of carbon black and
magnetite.
9. A process in accordance with claim 1 wherein the shell monomer
is a difunctional, trifunctional or oligomeric aromatic
isocyanate.
10. A process in accordance with claim 1 wherein the pigment
particles are dispersed by a ball milling process.
11. A process in accordance with claim 1 wherein the pigment
particles are dispersed in the core materials by a high shear
mixing method.
12. A process in accordance with claim 1 wherein there is further
included in the reaction components a reinforcing agent present in
the core, thereby enabling minimization of smear and the
optimization of the fixing properties of the images generated.
13. A process in accordance with claim 7 wherein the magnetite is a
mixture of iron oxides.
14. A process in accordance with claim 9 wherein the oligomeric
materials are formed insitu within the core materials.
15. A process in accordance with claim 1 wherein the elastomeric
polymer is selected from the group consisting of polyisobutylene,
polybutadiene, polybutenes, polyisoprenes, polysiloxanes, and
copolymers of the aforementioned compositions.
16. A process in accordance with claim 15 in wherein the copolymer
is poly(styrene-butadiene).
17. An imaging process which comprises the formation of an
electrostatic latent image on an imaging surface, followed by
developing this image with the toner composition obtained from the
process of claim 1, thereafter transferring the image to a suitable
substrate, and affixing the image thereon.
18. An imaging process in accordance with claim 17 wherein the
toner selected contains therein magnetite.
19. An imaging process in accordance with claim 17 wherein toner
selected contains wherein carbon black.
20. An imaging process in accordance with claim 17 wherein fixing
is accomplished by pressure rollers maintained at a pressure of
from about 80 to about 200 pounds per linear inch.
21. A process in accordance with claim 1 wherein the water
insoluble organic solvent is a hydrocarbon or mixtures thereof with
a boiling point above room temperature and below about 80 degrees
Centigrade.
22. A process in accordance with claim 21 wherein the solvent is
selected from the group consisting of cyclohexane, dichloromethane,
and 1,1,1 trichloroethane.
23. A process in accordance with claim 1 wherein the stabilizing
materials are selected from the group consisting of poly(vinyl
alcohols), hydroxypropylcellulose, poly(ethylene oxide-co-propylene
oxide) and hydroxyethyl cellulose.
24. A process in accordance with claim 1 wherein there are added to
the reaction mixture additive particles.
25. A process in accordance with claim 24 wherein the additive
particles are comprised of colloidal silicas.
26. A process for the preparation of cold pressure fixable toner
compositions which comprises (1) dispersing carbon black in an
amount of from about 5 percent to about 30 percent by weight in an
organic solution comprised of a mixture of cyclohexane and
dichloromethane, adding an elastomer of polyisobutylene thereto in
an amount of from about 30 to about 50 percent by weight of the
final toner, and subsequently dispersing therein magnetite in an
amount of from 1 to about 20 percent by weight; (2) thereafter
adding shell monomers in an amount of from about 10 to about 45
percent by weight, and tris(p-iscyanato-phenyl)thiophosphate; (3)
dispersing the resulting mixture in water, in an amount of from
about 5 to about 45 percent by volume containing from about 0.2 to
about 2 percent by weight of a surfactant stabilizer; (4)
subsequently heating the reaction mixture at a sufficient
temperature of from about 35 to about 70 degrees Centigrade to
permit hydrolysis; and thereafter heating the resulting mixture at
a temperature of from about 70 to about 90 degrees Centigrade,
enabling further hydrolysis and an interfacial polymerization
reaction thereby allowing the formation of a hard shell; (5)
subsequently washing the resulting toner composition for a
sufficient period of time that will enable substantially no
residual surfactant to remain in the water; and (6) thereafter
spray drying the washed toner composition product thereby yielding
a free flowing toner powder.
27. A process in accordance with claim 26 wherein the shell monomer
is toluene diisocyanate.
28. A process in accordance with claim 26 wherein there is added to
the shell monomer tris(p-isocyanato-phenyl)thiophosphate in an
amount of from about 0.5 percent to about 10 percent by weight.
29. A process in accordance with claim 21 wherein there are added
to the reaction mixture additive particles.
30. An imaging process which comprises the formation of an
electrostatic latent image on an imaging surface, followed by
developing this image with the toner composition obtained from the
process of claim 26, thereafter transferring the image to a
suitable substrate, and affixing the image thereon.
Description
BACKGROUND OF THE INVENTION
The present invention is generally directed to processes for the
preparation of cold pressure fixable toner compositions, and more
specifically the present invention is directed to processes for
obtaining single and/or two component cold pressure fixable toner
compositions comprised of a core of carbon black, and a tough
polymeric shell generated by an interfacial polymerization process,
wherein the shell monomer is dissolved in the core prior to
polymerization. Accordingly, in an embodiment of the present
invention there are provided processes for formulating in an
economical, and simple manner cold pressure fixable toner
compositions by dispersing or dissolving the shell components in
the core material selected for the toner, followed by hydrolysis,
and subsequently an interfacial polymerization. The toners
resulting are useful for permitting the development of images in
electrostatographic imaging systems, inclusive of electrostatic
imaging processes wherein pressure fixing, especially pressure
fixing in the absence of heat is selected.
Cold pressure fixing processes are known. These processes have a
number of advantages in comparison to heat fixing, primarily
relating to the requirements for less energy since the toner
compositions used can be fused at room temperature. Nevertheless,
many of the prior art cold pressure fixable toner compositions
suffer from a number of deficiencies. For example, these toner
compositions must usually be fused under high pressure, which has a
tendency to severely disrupt the toner fusing characteristics of
the toner selected. This can result in images of low resolution, or
no images whatsoever. Also, in some of the prior art processes
substantial image smearing can result from the high pressures
required. Additionally, the cold pressure fixing toner compositions
of the prior art have other disadvantages in that, for example,
these compositions when used for development cause in some
instances images with high gloss that are of low crease resistance.
Furthermore, the images resulting exhibit an undesirable carbon
paper effect, thus there is a total or partial image transfer from
the image substrate to neighboring substrates caused by pressures
arising from normal handling. In contrast, images developed with
the cold pressure compositions prepared in accordance with the
process of the present invention posses a low gloss appearance on
plain paper, and further there is no carbon paper effect observed.
Also, the toner compositions prepared in accordance with the
process of the present invention have hard shells thus enabling
images of excellent resolution with substantially no background
deposits. Accordingly, with the process of the present invention
inner polymerization methods permit the formation of aromatic
polyurea shells, that is polymers wherein the main chains are
comprised of aromatic groups. These polymers possess different
characteristics, for example they are tougher and stronger than
several prior art shells prepared by the interfacial polymerization
of, for example, an aromatic or aliphatic oil soluble component
with a water soluble aliphatic amine or alcohol. Furthermore, when
shells are prepared from water soluble aromatics, such as phenol
derivatives, it is often necessary to use solutions of a high pH
value. This adversely affects the interfacial polymerization and
the efficiency of added surfactants such as poly(vinylalcohol).
When the efficiency of the surfactants is decreased, it is
difficult to prepare toner particles with the appropriate diameter
for use in imaging processes, and in addition agglomeration of the
particles results.
With further reference to the prior art, there is disclosed in U.S.
Pat. No. 4,307,169 microcapsular electrostatic marking particles
containing a pressure fixable core, and an encapsulating substance
comprised of a pressure rupturable shell, which shell is formed by
an interfacial polymerization. One shell prepared in accordance
with the teachings of this patent is a polyamide obtained by
interfacial polymerization. In the U.S. Pat. No. 4,307,169, it is
indicated that when magnetite or carbon black is selected they must
be treated in a separate process to prevent migration thereof to
the oil phase.
Interfacial polymerization processes are described in British
Patent Publication No. 1,371,179, the disclosure of which is
totally incorporated herein by reference, which publication
illustrates a method of microencapsulation based on in situ
interfacial condensation polymerization. More specifically, this
publication discloses a process which permits the encapsulation of
organic pesticides by the hydrolysis of polymethylene
polyphenylisocyanate, or toluene diisocyanate monomers. There is no
teaching, however, in the '179 publication relating to a process
for preparing cold pressure fixable two component toners. Also, the
wall forming reaction disclosed in the aforementioned publication
is initiated by heating the mixture to an elevated temperature at
which point the isocyante monomers are hydrolized at the interface
to form amines, which in turn react with unhydrolized isocyanate
monomers to enable the formulation of a polyurea microcapsule wall.
One difficulty associated with the process of the '179 publication
resides in the possibility of the continued reaction of monomer
after packaging. Therefore, unless the monomer selected is reacted
during the preparation, there will be continued hydrolysis with
evolution of carbon dioxide resulting in the formation of pressure.
This problem, which is overcome with the process of the present
invention, is also illustrated in European Patent Application No.
84870186.8. Furthermore, with the process of the present invention
the appropriate solvent selection (the amount of, for example,
isocyanate shell materials used), the improved control of the
hydrolysis reactions being accomplished as determined by an
analysis of the kinetics thereof, and the design of a suitable
reaction temperature profile enable the formation of toners with
acceptable levels of residual isocyanates, that is no monomers are
detectable by thermogravimetric analysis at the highest sensitivity
setting. The process of the present invention also permits the
controlled formation of oligomers which impart improved fusing
characteristics to the resulting toner compositions. Additionally,
with the process of the present invention the disadvantages of the
post-treatment of the toner compositions prepared under controlled
conditions are prevented thereby avoiding continued evolution of
carbon dioxide, and excessive aggregations.
Furthermore, there is disclosed in U.S. Pat. No. 4,552,811, a
process for capsule formation by an an inner polymerization
process. In this process, the reactants forming the interfacial
materials are dispersed in the water phase, and not in an organic
phase.
Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the
disclosure of which is totally incorporated herein by reference,
interfacial polymerization processes for pressure sensitive toner
compositions comprised of a blend of two immiscible polymers
selected from the group consisting of certain polymers as a hard
component, and polyoctyldecylvinylether-co-maleic anhydride as a
soft component.
Additionally, illustrated in a copending application U.S. Ser. No.
621,307, entitled Single Component Cold Pressure Fixable
Encapsulated Toner Composition, the disclosure of which is totally
incorporated herein by reference, are single component cold
pressure fixable toner compositions, wherein the shell selected can
be prepared by an interfacial polymerization process. A similar
teaching is present in copending application U.S. Ser. No. 718,676,
the disclosure of which is totally incorporated herein by
reference, directed to single component magnetic cold pressure
fixable toner compositions. In the aforementioned application, the
core can be comprised of magnetite and a polyisobutylene of a
specific molecular weight encapsulated in a polymeric shell
material generated by an interfacial polymerization process. More
specifically, there is illustrated in the aforementioned copending
application cold pressure fixable magnetic single component
developers with small amounts of carbon black and large amounts of
magnetite.
Furthermore, other prior art that might be of background interest
includes U.S. Pat. Nos. 4,254,201; 4,465,755; 4,520,091; and
Japanese Patent Publication No. 58-100857. The Japanese publication
discloses a capsule toner with high mechanical strength, which is
comprised of a core material including a display recording
material, a binder, and an outer shell enclosing the core material,
which outer shell is preferably comprised of a polyurea resin. In
the U.S. Pat. No. 4,520,091, there is disclosed encapsulated
electrostatographic toners wherein the shell material comprises at
least one resin selected from polyurethane resins, a polyurea
resin, or a polyamide resin. In addition, the U.S. Pat. No.
4,465,755 discloses a pressure fixable toner comprising
encapsulated particles containing a curing agent, and wherein the
shell is comprised of a polyurethane, a polyurea, or a
polythiourethane. Moreover, in the U.S. Pat. No. 4,254,201 there is
illustrated pressure sensitive adhesive toners comprised of
clustered encapsulated porous particles, which toners are prepared
by spray drying an aqueous dispersion of the granules containing an
encapsulated material.
Accordingly, there is a need for improved processes that will
enable cold pressure fixable toner compositions with hard shells.
Also, there is a need for improved processes that will permit the
formulation of cold pressure fixable toner compositions with carbon
black, or magnetite as the core material. There is also a need for
improved processes that will enable cold pressure fixable toner
compositions with mixtures of carbon black and magnetite as the
core material. Additionally, there is a need for simple economical
interfacial polymerization processes that will allow hard shells to
be generated for cold pressure fixable toner compositions. There is
also a need for improved processes that will provide cold pressure
fixable toner compositions with hard shells, and wherein the
monomer selected for the shell is dissolved in the core. Moreover,
there is a need for a process that permits the selected control of
the toner electrical properties, inclusive of dielectric constant
characteristics, and triboelectrics charging properties. The
aforementioned properties, and characteristics properties are
dependent primarily on the type of carbon black dispersion, and the
carbon black loading.
Another advantage associated with the process of the present
invention resides in the ability to control the shell properties
thereby permitting, for example, desirable toner properties
inclusive of appropriate toner particle size, and acceptable fixing
and smear properties. Indirectly, there is also permitted in
accordance with the process of the present invention the monitoring
of small changes in core properties, such as the viscosity thereof,
and the pigment dispersion characteristics. The aforementioned
advantages are demonstrated hereinafter, and in particular in
Example X.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide processes for
cold pressure fixable toner compositions which overcome many of the
above-noted disadvantages.
In another object of the present invention there are provided
processes for cold pressure fixable toner compositions with hard
shells formulated by an improved interfacial polymerization
process.
Also, in a further object of the present invention there are
provided processes for cold pressure fixable toner compositions
with hard shells, wherein the shell monomer is dissolved in the
core component selected.
Further, an additional object of the present invention resides in
simple and economical processes for the preparation of cold
pressure fixable toner compositions with hard shells formulated by
an improved hydrolysis, and interfacial polymerization process.
An additional object of the present invention resides in the
provision of a cold pressure fixable toner with optimized smear and
fix properties, obtained as a result of, for example, the
controlled additions of small amounts, preferably between 1 and
about 10 percent by weight of reinforcing agents, such as a
polymeric material, thus causing a modification of the rheological
properties of the toner core composition prepared from elastomer
components.
Additionally, in another object of the present invention there are
provided carbon black or magnetite based cold pressure fixable
toner composition.
In yet still another object of the present invention there are
provided encapsulated toners with a substantially uniform thickness
for the protecting shell.
In another object of the present invention there are provided
carbon black based cold pressure fixable toner with improved
blocking and fusing characteristics.
These and other objects of the present invention are accomplished
by the provision of processes for the formulation of cold pressure
fixable toner compositions with an improved interfacial
polymerization. More specifically, there is provided in accordance
with the present invention a process for the preparation of cold
pressure fixable toner compositions wherein a hard shell component
is obtained by hydrolysis and interfacial polymerization. In
another embodiment of the present invention the process comprises
the formulation of a tough aromatic polyurea shell, that is a shell
that will withstand most toner manufacturing process, especially
spray drying a processes; and also wherein there can be formulated
a substantially unbreakable or uncrackable shell. With the process
of the present invention, in one important aspect thereof the shell
monomer is dissolved in the toner core of carbon black, or mixtures
of carbon black and magnetite.
In addition, there is provided in accordance with the present
invention a process for the preparation of cold pressure fixable
toner compositions which comprises (1) admixing a core component
comprised of pigment particles, a water insoluble organic solvent
and elastomeric materials and a shell monomer dissolved therein;
(2) dispersing the resulting mixture in a water phase containing a
stabilizing material; (3) hydrolyzing by heating the resulting
mixture; (4) subsequently affecting an interfacial polymerization
of the aforementioned mixture; and (5) thereafter optionally
washing the resulting toner composition.
More specifically, the process of the present invention involves
the preparation of cold pressure fixable toner compositions which
comprises (1) admixing a core component comprised of pigment
particles in an amount of from about 5 to about 30 percent by
weight of the final toner, a wate insoluble organic solvent and,
for example, polyisobutylene elastomeric materials in an amount of
from about 30 to about 50 percent by weight of the final toner with
a shell monomer dissolved therein in an amount of from about 10 to
about 45 percent by weight of the final toner; (2) dispersing the
resulting mixture in a water phase containing a stabilizing
material; (3) hydrolyzing the resulting mixture by heating, for
example, at a temperature of from about 35 to about 70 degrees
Centigrade; (4) subsequently affecting interfacial polymerization
thereof by heating the mixture resulting from, for example, about
70 to 90 degrees Centigrade; and (5) thereafter washing the toner
product obtained. The aforementioned washing is accomplished
primarily for the purpose of causing the removal of stabilizing
materials, and further the toner product obtained can be
subsequently dried preferably utilizing spray drying processes.
In one specific embodiment of the present invention, the process
comprises (1) dispersing carbon black in an amount of from about 5
percent to about 30 percent by weight in an organic solution
comprised of a mixture of cyclohexane and dichloromethane, adding
an elastomer of polyisobutylene thereto in an amount of from about
30 to about 50 percent by weight of the final toner, and
subsequently dispersing therein magnetite in an amount of from 1 to
about 20 percent by weight; (2) thereafter adding shell monomers,
such as toluene diisocyanate in an amount of from about 10 to about
45 percent by weight, and tris(p-isocyanato-phenyl)thiophosphate,
in an amount of from about 0.5% percent to about 10 percent by
weight; (3) dispersing the resulting mixture in water in an amount
of from about 5 to about 45 percent by volume containing from about
0.2 to about 2 percent by weight of poly(vinyl alcohol) or a
similar surfactant stabilizer, preferably by using a shear
homogenizer; (4 ) subsequently heating the reaction mixture at a
sufficient temperature to permit hydrolysis, preferably from about
35 to about 70 degrees Centigrade; and thereafter heating at a
higher temperature, preferably from about 70 to about 90 degrees
Centigrade, enabling further hydrolysis and interfacial
polymerization, thereby allowing the formation of a hard polyurea
shell; (5) subsequently washing the resulting toner with distilled
water for a sufficient period of time that will enable
substantially no residual poly(vinyl alcohol) to remain in the
water; and (6) thereafter spray drying the washed toner composition
product thereby yielding a free flowing toner powder. Additionally,
in accordance with the process of the present invention there can
be added to the toner composition obtained optional additive
particles, such as from about 0.2 to 2 percent by weight, and
preferably from about 0.2 to about 1.0 percent by weight of a flow
agent. Examples of flow agents that may be selected are Aerosils,
reference U.S. Pat. No. 3,900,588, the disclosure of which is
totally incorporated herein by reference, such as Aerosil R972,
Aerosil R974, and the like, available from Degussa Canada Ltd..
Also, the size diameter of the resulting particles can be
controlled effectively from about 5 microns to 50 microns, and
preferably from 10 microns to 30 microns, which size depends, for
example, on such parameters as the nature and concentration of the
surfactant used, the homogenizer type and speed, the nature and
amount of reinforcing agent, the initial core viscosity prior to
the dispersion of the organic phase into the water phase, the ratio
of organic to water phase, the temperature, and the nature of the
solvent used to solubilize the core polymer. Therefore, the
resulting toner can contain in the core carbon black and/or
magnetite dispersed in a polymeric matrix of polyisobutylene, and
an optional polymeric reinforcing agent in an amount of from about
1 to about 10 percent, such as a block copolymer of styrene
butadiene, available as Kraton, the primary function of which is to
increase the elastomer compression modulus. Other examples of
reinforcing agents include styrene-butadiene (Kraton) diblock
copolymers. The toner may also contain as compression modulus
modifiers in various effective amounts, such as for example from
about 5 to about 50 percent by weight, styrene-isoprene diblock
copolymers, styrene-isoprene-styrene triblock polymers,
alpha-methylstyrene-butadiene diblock copolymers,
alpha-methylstyrene-butadiene-alpha-methylstyrene triblock
copolymers, and the like.
Illustrative examples of elastomers that may be selected for the
process of the present invention are polyisobutylene,
polybutadiene, polybutenes, polyisoprenes, polysiloxanes,
copolymers of the aforementioned compositions, inclusive of
poly(styrene-butadiene); and other similar equivalent polymers such
as those with the same, or a similar compression modulus.
Illustrative examples of carbon black core components include
carbon blacks available from Cabot, Degussa, Capuava and Columbian
carbon blacks such as Regal.RTM. 330, Vulcan XC-72R, Raven 5750,
5250 and 5250B, 3500 and 3200, Printex type carbon blacks, and
N-326 type from Capuava. It is preferable to use high surface area
carbon blacks in the process described therein. The carbon black
can be present in an amount of from about 5 percent by weight to
about 30 percent by weight
Magnetites that can be selected are commercially available as
MO-7029, MO-8029, and MO-4431 from Pfizer Corporation; Mapico Black
from Columbia Inc.; Bayferrox magnetites from Mobay Chemical, and
the like. The magnetites, which are admixed with the carbon black,
are present in an amount of from about 1 percent by weight to about
20 percent by weight.
Examples of shell materials include toluene diisocyanates,
isophthaloyl chloride, m-phenylenediisocyanate, naphthalene-1,4,
diisocyanate or other aromatic isocyanate substituted of the same
family. Included in this family are tri-, tetra-, and
polyisocyanate prepolymers capable of providing hard shells by an
in-situ interfacial polymerization process as described herein.
Surfactants or emulsion stabilizers, in an amount of from about 0.2
to about 2 percent that may be selected for the process of the
present invention are poly(vinyl alcohol), hydroxypropyl cellulose,
poly(ethylene oxide-co-propylene oxide), hydroxyethylcelluloses,
and the like.
Illustrative examples of solvents selected for the process of the
present invention include known organic solvents such as
hydrocarbons inclusive of cyclohexane, dichloromethane, 1,1,1
trichloroethane, and other similar solvents of a boiling point
below about 80.degree. C.
Final properties of the toner prepared by the process of the
present invention are also dependent on the following process
parameters: (1) the temperature at which the hydrolysis occurs as
well as the temperature profile thereof, which temperature can vary
from about 20.degree. C. to about 90.degree. C., and preferably is
between 55.degree. C. and 70.degree. C. Different temperature
profiles are applicable to the process, preferably the first stage
of the process must include a period of time during which the
temperature is increased very slowly in order to control foaming
due to the gas evolution during the hydrolysis; and (2) the mixing
times are critical in determining in the first stage the extent of
carbon black dispersion in the organic phase and secondly, the
final particle size. X-ray can be used to obtain inner surface area
(Os) data on carbon black containing toners. In that context, Os
values can give indications of the quality of the dispersions.
Values ranging from 13 to 28 meters square per centimeter cube were
obtained for encapsulated toners containing 20 to 24 percent carbon
black. Larger inner surface area values are indication of better
carbon black dispersion all other factors being the same. When
toners are prepared by more standard methods such as melt blending
these values are obtained with much less than 10 percent loading.
It is known that within the above range of Os values, the above
discussed electrical properties of the present invention can vary
by about 20 percent. It is believed that encapsulation technology
allows control of these variations at higher loading of carbon
black.
The following examples are being submitted to further define
various species of the present invention. These examples are
intended to be illustrative only and are not intended to limit the
scope of the present invention. Also, in the Examples parts and
percentages are by weight unless otherwise indicated.
EXAMPLE I
There was prepared a carbon black encapsulated toner as follows:
Raven 5250 carbon black, 12 grams, polyisobutylene, Vistanex LMMH
(Exxon), 22.0 grams, cyclohexane ACS (Caledon), 120.0 grams, and 5
millimeters (diameter) ball bearings (1/3 of total volume) were
placed in a 250 milliliters plastic bottle and ball milled for 24
hours. Toluene diisocyanate (Olin Chemicals, type TD1-80), 10
grams, and Desmodur RF, a triisocyanate crosslinking agent from
Bayer, 25 milliliters in dichloromethane, 20 milliliters, were
added to 97.5 grams of the previously prepared mixture (without any
ball bearings). The mixture was then homogenized by shaking in a
capped plastic bottle for 20 seconds. Thereafter, the contents of
the plastic bottle were added to a mixture of 0.75 percent
poly(vinyl alcohol) (Scientific Polymer Products), 500 milliliters,
and 2-decanol, 0.5 milliliters, followed by dispersion with a
Brinkmann PT 45/80 homogenizer and a PT 35/4 generator for 15
seconds at 6500 rpm. Subsequently, the resulting mixture was
transferred to a 2 liter beaker equipped with a mechanical stirrer,
and an oil bath under the beaker. The mixture was then heated at
50.degree. C. for three hours during which time a polymerization
reaction took place to form a polyurea shell. Thereafter, the
temperature was increased to 68.degree. C. for 16 hours permitting
reaction completion and removal of cyclohexane and dichloromethane.
The reaction mixture was then allowed to stabilize at room
temperature, and the toner composition resulting was washed with
water, and settled using an lEC-B20A centrifuge for 12 minutes at
8,000 rpm. This procedure was repeated three times. The washed
toner was then filtered through a 212 micron screen filter to
remove any aggregates, followed by spray drying in a Buchi model
190 spray dryer at an inlet temperature of 120.degree. C. and
outlet temperature of 94.degree. C. The average particle size of
the resulting toner particle product was 13.5 microns with a GSD of
1.40 as determined with a Coulter counter. After the addition of 1
percent by weight of Aerosil R972, available from Degussa Canada
Ltd., this toner could be imaged on a flat plate test fixture with
an Ektaprint L organic photoreceptor belt (green type), available
from Eastman Kodak. After fusing with a Hitachi three-roll fuser
set at 2000 psi, the images exhibited strong crease and smear
resistance. Furthermore, subsequent to the rubbing of the images
obtained with fingers, it was found that there was essentially no
smearing of the images, that is there was no deterioration of the
image resolution and no toner was removed from the paper onto the
finger.
Crease was determined qualitatively by folding the image under
reproducible conditions and examining the crease area visually with
an optical microscope. The width of the crease and the residual
toner amount in the crease area can give a relative estimate of the
crease quality. The aforementioned cold pressure fixable toner had
better creae properties than a standard heat fusible toner
comprised of a styrene n-butylmethacrylate resin, 90 percent by
weight, and carbon black particles, 10 percent by weight, in that
the amount of residual toner present in the crease area was always
larger, about 50 percent more for the above prepared cold pressure
fixable toner as compared to the aforementioned standard toner.
EXAMPLE II
A carbon black encapsulated toner was prepared by admixing a
dispersion of the carbon black pigment, Raven 5250 (8 parts),
toluene diisocyanate (10 parts) and
tris(p-isocyanate-phenyl)thiophosphate (1 part a triisocyanate
crosslinker sold under the trade name Desmodur RF) in a solution of
polyisobutylene (Vistanex LMMH) (12 parts) in a mixture of
cyclohexane (20 parts) and dichloromethane (30 parts). The organic
component thus prepared was dispersed into water (300 parts)
containing 0.75 percent poly(vinyl alcohol) by a high shear
homogenizer polytron. The reaction mixture was then transferred to
a reactor equipped with a mechanical stirrer. Shell formation was
affected by raising the temperature to 55.degree. C. for 3 hours
and subsequently to 75.degree. C. for another 5 hours. The capsules
are washed with water and spray dried under conditions similar to
those described in Example I. The reactive ingredients, the di- and
tri-isocyanates are in the core phase. The shell material is formed
when the reaction temperature is raised to promote the hydrolysis
of the isocyanate functions to amine groups at the interface which
in turn react with the remaining isocyanate groups to yield an all
aromatic polyurea shell. The resulting dried toner has acceptable
blocking temperature greater than 50.degree. C. Tribo blow-off
measurements reveal that the toner charges to a +30 microcoulombs
per gram against a carrier core consisting of iron oxide, and a
terpolymer mixture of styrene, methylmethacrylate and vinyl
triethoxy silane. Powder cloud images of this toner, that is images
prepared by overlaying controlled amounts of toners on a piece of
paper (stencils were used in order to obtain different image
patterns), were fixed using a Hitachi three-roll fuser set at about
2,000 psi (125 pli) yield images with excellent fix, that is the
ratio of optical density before and after a Taber abrasion test of
0.54 was measured based on a standard optical density of 1.0. In
addition, the image exhibits strong crease and smear resistance
when tested under the condition described in Example I.
EXAMPLE III
A carbon black encapsulated toner was prepared as follows: Vistanex
LMMH, 20.7 grams, Kraton DX-1115, 1.32 grams, a styrenebutadiene
triblock polymer (Shell) were dissolved in cyclohexane 120 grams.
To help speed up the dissolving process, the contents were shaken
on a wrist shaker for 12 hours. Raven carbon black 5250-B, 12.0
grams, was added to the solution, and the mixture was homogenized
using a Brinkmann PT 45/80 homogenizer with a PT 20 generator for a
period of 4 minutes at 9,000 rpm. The mixture was cooled in a water
bath while being homogenized. Furthermore, the homogenizing time
was not continuous, the homogenizer was run in period of 1 minute
with 1 minute of resting time. TDI-80, 10.0 grams, Desmodur RF, 25
milliliters, and dichloromethane, 20 milliliters, were added to the
previous mixture and homogenized with a PT 45/80 homogenizer and a
PT-20 generator for 1 minute at 9000 rpm (cooled). The mixture was
added to 0.75 percent poly(vinyl alcohol), 500 milliliters, and
2-decanol, 0.5 milliliter, and dispersed for 20 seconds at 7,500
rpm using a PT 45/80 homogenizer and a PT 35/4 probe generator. The
reaction mixture was transferred to a 2 liter beaker equipped with
a mechanical stirrer and an oil bath was placed under it. The
mixture was stirred and heated at 50.degree. C. for three hours,
during this time hydrolysis of the isocyanate groups and an
interfacial polymerization reaction took place to form a polyurea
shell. The mixture continued to stir at 69.degree. C. for the next
half day. This removed some of the cyclohexane and dichloromethane
from the mixture and allowed further interfacial polymerization. A
model study of the hydrolysis phenomena, which results in the
disappearance of the isocyanate groups was done at three different
temperatures, 50.degree. C., 60.degree. C. and 70.degree. C., under
conditions which approximate those under which the toner particles
are prepared. The percent NCO content was monitored by a titration
method. Graphs of percent NCO (for toluene diisocyanate) reacted
versus time (seconds) were plotted to give linear relationships.
Pseudo zero rate constants (k) were calculated for each
temperature. These were 4.2.times.10-3, 6.8.times.10-3 and
9.6.times.10-3 percent per second at 50, 60, 70.degree. C.,
respectively. The hydrolysis was expected to be a first order
reaction with respect to the concentration of isocyanate. In
contrast, since the changes in total concentration of isocyanates
were monitored, and not the changes in total concentration of
isocyanates in the water and/or the organic phase, it is possible
that the reaction appeared to be of zero order as in this case. The
rate constants were also used to calculate the activation energy
(Ea) for the reaction using an Arrhenius type plot. Ea was found to
be 39.7 kilojoules. Zero order rate constants are usually expressed
in units of moles per liter per second (moles L.sup.-1 S.sup.-1).
Because of variations in solution volumes, especially at 70.degree.
C., no attempts were made to calculate the exact concentration of
isocyanate groups in moles/liter of organic phase and the
calculated percent NCO reacted values were used to determine the
reported empirical zero order rate constants above. Knowledge of
the rate constants and activation energy allowed the prediction of
the consumption rate of isocyanate groups via hydrolysis at any
chosen temperature. The toner was washed three times with water,
each time being settled using an lEC-B20A centrifuge at 8,000 rpm
and for a period of 12 minutes. A 212 microns screen filter was
used to remove any aggregates. The toner was spray dried with a
Buchi 190 spray dryer with an inlet temperature of 120.degree. C.
and an outlet temperature of 95.degree. C. The average particle
size of this toner was 13.8 microns and its geometric standard
deviation (GSD) of 1.30 as determined with a Coulter counter. This
sample contains 2.6 percent Kraton DX 1115. The fix level for the
toner prepared in accordance with this Example was 0.40 as measured
by recording the optical density prior to, and subsequent to the
known Taber Abrasion test at 100 pli pressure.
EXAMPLE IV
A carbon black encapsulated toner was prepared by repeating the
procedure of Example III with the exceptions that 1) 0.9 percent
Kraton was used instead of 2.6 percent of Kraton, and 2) the oil
phase mixture was added to 0.75 percent poly(vinyl alcohol), 500
milliliters, and 2-decanol, 0.5 milliliters, and dispersed for 20
seconds at 6,500 rpm instead of 7,500 rpm using a Brinkmann PT
45/80 homogenizer and a PT 35/4 probe generator. The average
particle size of the resulting toner was 15.2 microns and its
geometric standard deviation (GSD) of 1.47 as determined with a
Coulter counter.
EXAMPLE V
A carbon black encapsulated toner was prepared by repeating the
procedure of Example III with the exception that the oil phase
mixture was added to 0.75 percent poly(vinyl alcohol), 500
milliliters, and 2-decanol, 0.5 milliliters, and dispersed for 20
seconds at 6,500 rpm instead of 7,500 rpm using a Brinkmann PT
45/80 homogenizer and a PT 35/4 probe generator. The average
particle size of this toner was 18.4 microns and its geometric
standard deviation was 1.40 as determined with a Coulter
counter.
EXAMPLE VI
A carbon black encapsulated toner was prepared by repeating the
procedure of Example IV with the exception that 1.7 percent instead
of 0.9 percent Kraton DX-1115 was used as part of the core
component, and the oil phase mixture was added to 0.75 percent
poly(vinyl alcohol), 500 milliliters, and 2-decanol, 0.5
milliliters, and dispersed for 15 seconds instead of 20 seconds at
6,500 rpm using a Brinkmann PT 45/80 homogenizer and a PT 35/4
probe generator. The average particle size of this toner was 17.0
microns and its geometric standard deviation (GSD) of 1.36 as
determined with a Coulter counter. This toner was part of the
series of toners of variable compression modulus and fix level as
the proportion of Kraton DX-1115 was varied from 0 to 2.6 percent.
The fix level for the toner prepared in accordance with this
Example was 0.43 as measured by recording the optical density prior
to, and subsequent to the known Taber Abrasion test at 100 pli
pressure.
EXAMPLE VII
A carbon black encapsulated toner was prepared by repeating the
procedure of Example IV with the exception that no Kraton DX-1115
was used as core component. The average particle size of the final
toner was 15.6 microns and its geometric standard deviation of 1.41
as determined with a Coulter counter. The fix level for the toner
prepared in accordance with this Example was 0.54 as measured by
recording the optical density prior to, and subsequent to the known
Taber Abrasion test at 100 pli pressure.
EXAMPLE VIII
A carbon black encapsulated toner was prepared by repeating the
procedure of Example I with the exception that the organic phase
was added to 0.75 percent poly(vinyl alcohol), 500 milliliters, and
2-decanol, 0.5 milliliters. This was dispersed using a Brinkmann PT
45/80 homogenizer and a PT 35/4 generator for 10 seconds instead of
15 seconds at 6,500 rpm. The average particle size of the toner
product was 16 microns and the GSD was 1.50 as determined with a
Coulter counter. Powder cloud images prepared from this toner in a
manner identical to the one described in Example II, were fixed
using a Hitachi three roll fuser set at 125 pli yielding excellent
fix, that is the ratio of optical density before and after a Taber
Abrasion test was about 0.5 based on a standard optical density of
1.0. In addition, the images exhibit similar crease and smear
resistance as the images of Example I.
EXAMPLE IX
A carbon black colored encapsulated toner was prepared as follows:
Vistanex LMMH, 22.0 grams, was dissolved in cyclohexane, 120 grams.
To help speed up the dissolving process, the contents were shaken
on a wrist shaker for 12 hours. Raven carbon black 5250-B, 12.0
grams, was added to the solution, and the mixture was homogenized
using a Brinkmann PT 45/80 homogenizer with a PT 20 generator for a
period of 4 minutes at 9,000 rpm. The mixture was cooled in a water
bath while being homogenized. Furthermore, the homogenizing time
was not continuous; the homogenizer was run in periods of 2 minutes
with 1 minute of resting time. TDl-80, 15.8 grams, Desmodur RF, 40
milliliters, and dichloromethane, 20 milliliters, were added to the
previous mixture and homogenized with a PT 45/80 homogenizer and a
PT-20 generator for 1 minute at 9,000 rpm (cooled). The mixture was
added to 0.75 percent poly(vinyl alcohol), 500 milliliters, and
2-decanol, 0.5 milliliters, and dispersed for 15 seconds at 6,500
rpm using a PT 45/80 homogenizer and a PT 35/4 probe generator. The
reaction mixture was transferred to a 2 liter beaker equipped with
a mechanical stirrer and an oil bath was placed under it. The
mixture was stirred and heated at 47.5.degree. C. for three hours,
during this time an interfacial polymerization reaction took place
to form a polyurea shell. The mixture continued to stir at
65.degree. C. for the next half day. This removed some of the
cyclohexane and dichloromethane from the mixture and allowed
further interfacial polymerization. The toner was washed three
times with water, each time being settled using an IEC-B20A
centrifuge at 8,000 rpm and for a period of 12 minutes. A 212
microns screen filter was used to remove any aggregates. The toner
was spray dried with a Buchi 190 spray dryer at an inlet
temperature of 124.degree. C. and an outlet temperature of
94.degree. C. The average particle size of this toner was 15.6
microns, and its geometric standard deviation (GSD) of 1.41 as
measured with a Coulter counter. After addition of Aerosil R972,
Degussa Canada Ltd., this toner was imaged on a flat plate fixture
system using a selenium photoreceptor. After fusing with a Hitachi
three-roll fuser set at 2,000 psi, the images exhibited strong
crease and smear resistance similar to the images of Examples I and
II.
Other modifications of the present invention may occur to those
skilled in the art based upon a reading of the present disclosure,
and these modifications are intended to be included within the
scope of the present invention.
* * * * *